1. Field of the Invention
The invention relates to a medical charged particle irradiation apparatus for using charged particles to treat cancer, lump and so on.
2. Description of the Related Art
A medical charged particle irradiation apparatus for irradiating charged particles such as proton, carbon ion, or the like on an affected part of a patient to treat cancer, lump and so on injects charged particles, which are generated in an ion source and accelerated by a synchrotron or the like, to guide the same to an irradiation field forming means containing a collimator or the like, and irradiates the charged particles on a patient lying below the irradiation field forming means after an irradiation field conformed to a configuration of the affected part is formed in the irradiation field forming means.
At this time, a patient ordinarily lies on a patient's bed with the face upward, and it is necessary to perform irradiation from an appropriate angular position (for example, from upward or from substantially horizontally, or the like) in accordance with position and state of the affected part. Also, exposure dose from various directions is suppressed while irradiation is made on the affected part from a plurality of directions (multiple-field), whereby there is produced an effect that a predetermined exposure dose on the affected part can be achieved depending upon a weight of the part and exposure dose on other portions than the affected part can be lowered to reduce unnecessary exposure.
For example, Japanese Patent Laid-Open No. 192419/1993 describes a rotary irradiation therapeutic device as a prior art taking account of the above. This device comprises a substantially cylindrical-shaped rotary frame, an outer periphery of which is rotatably supported by rollers, and which mounts therein transport means (deflecting device and vacuum duct), irradiation field forming means (beam adjusting device), and an irradiation chamber provided with a patient's bed (irradiation bed). The transport means injects charged particle beams at a diametrically central portion of the rotary frame to transport the same to the irradiation field forming means while swinging up the same toward a diametrically outer periphery. The irradiation field forming means is arranged on a diameter passing an axis of rotation of the rotary frame to cause beams to be injected diametrically inwardly of the rotary frame from a distal end of the transport means arranged on the outer periphery of the rotary frame and to form an irradiation field for the beams to cause the beams to be injected into the irradiation chamber. The irradiation chamber is rotatably (turnably on its axis) arranged (in other words, rotatable about an axis of rotation of the rotary frame) on a beam emission side position of the irradiation field forming means in the rotary frame to constantly maintain the patient's bed substantially horizontal irrespective of a rotating position of the rotary frame.
With such construction, in the case where it is desirable to irradiate beams from, for example, above the affected part in accordance with position and state of the affected part, the rotary frame is turned to position the transport means on an upper side and the irradiation chamber on a lower side to cause beams having been swung up substantially vertically upward from the diametrically central portion of the rotary frame to be passed downward to be irradiated on the patient's bed in the irradiation chamber disposed below the irradiation field forming means from above. Also. in the case where it is desirable to irradiate beams from, for example, laterally (horizontal direction) of the affected part, the rotary frame is turned to position the transport means on one lateral side (for example, lefthand) and the irradiation chamber on the other lateral side (for example, righthand) to cause beams having been swung up leftward from the diametrically central portion of the rotary frame to be passed horizontally from lefthand to righthand to be horizontally irradiated on the patient's bed in the irradiation chamber disposed rightwardly of the irradiation field forming means.
However, the above prior art involves the following problems.
That is, the prior art provides a construction, in which the rotary frame provided with the irradiation chamber capable of turning on its axis is turned in order to irradiate beams from above and in a horizontal direction in accordance with a position of the affected part or the like as described above. As a result, a heightwise position of the patient's bed is considerably varied as the irradiation chamber makes a circular motion (vertical movement) due to turning of the rotary frame. Concretely, since a rotating irradiation body provided with the transport means and the irradiation field forming means has a turning diameter of, for example, around 5 m, a distance, over which the patient's bed rises from a lowest position for irradiation from above to a lateral position for irradiation from horizontal irradiation, amounts to about 2.5 m corresponding to a radius of rotation.
With the above prior art, a moving capsule capable of following the positional variation of the patient's bed is separately provided in juxtaposition to one sense of an axial direction of the rotary frame to cope with the situation, and a physician (or a technician) performing the irradiation preparing/ascertaining work can get on the moving capsule to easily reach a position of the patient's bed for improvement in convenience. However, because of the need of providing such moving mechanism as the moving capsule separate from the rotary frame, the entire device becomes large in size (in particular, in the axial direction of the rotary frame) and the mechanism is made complex.